TAS-103 is a novel anti-cancer agent selected for clinical trials on the basis of several interesting characteristics: 1) inhibition of both topoisomerase I and II, 2) potent cytotoxicity in several model systems, 3) selectivity for solid tumors, and 4) weak cross resistance to other anti-cancer drugs. In this single institution phase I trial eligible patients were required to have advanced solid tumors that were refractory to standard therapy, have a good performance status (ECOG z2), and adequate hematologic, hepatic, and renal function. The purposes were to define the maximum tolerated dose and recommend a dose for further study, to define and characterize the toxicities of the drug and to determine the pharmacokinetic and pharmacodynamic behavior of TAS-103. The starting dose was 20mg/m2 and was based on preclinical toxicology. Doses were doubled until grade 2 toxicity was observed then increased by no more than 33%. At least 3 patients were treated at each dose level. Dose limiting toxicity was considered to be grade 4 hematologic toxicity or grade 3 non-hematologic toxicity. Intrapatient dose escalation was permitted.